The effects of pinealectomy on cell proliferation in lens epithelium of male Spague Dawley rats is to be evaluated by counting numbers of cell divisions or 3H-thymidine labeled nuclei upon whole-mount preparations, or by liquid scintillation spectrometry after tritiated thymidine administration. The organ cultured rat lens will also be employed to assay direct effects by pineal-derived products including homogenates and melatonin. Other hormones will also be assayed for mitogenic effects on the epithelium of the organ cultured lens.